JP2006295100A - Method of manufacturing rare earth sintered magnet and method of pulverizing raw alloy powder for sintered magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a rare earth sintered magnet suppressing the amount of a lubricant added to the utmost and obtaining a compact with high strength and a sintered magnet with high magnetic characteristics, and a method of pulverizing raw alloy powder for the sintered magnet. <P>SOLUTION: In manufacturing the rare earth sintered magnet, a lubricant is pulverized so that the particle size of the lubricant may be ≤1.5 times of the particle size of raw alloy powder to obtain lubricant particles. Then, it is added to the raw alloy powder and pulverized to obtain finely pulverized powder. Then, this finely pulverized powder is formed in a magnetic field to form a compact. This compact is sintered to obtain the rare earth sintered magnet. When adding the lubricant particles having a particle size of a prescribed size with respect to the particle size of the raw alloy powder to the raw alloy powder and pulverizing it like this, the lubricant is dispersed more uniformly. Thus, pulverization property of raw alloy in a pulverization process and orientation of the pulverized powder are improved. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a rare earth sintered magnet typified by an Nd—Fe—B system and a method for pulverizing a raw alloy powder for a sintered magnet.

Rare earth sintered magnets are widely used as high-performance magnets, and their demand is increasing with the miniaturization of various electronic devices and the increase of electronic devices in automobiles. In general, the higher the degree of orientation of the magnet, the higher the residual magnetic flux density. For this reason, a magnetic field is applied to the raw material powder at the time of molding, and pressure molding is performed with the raw material powder oriented (so-called magnetic field molding).
At this time, in order to improve the orientation of the raw material powder with respect to the magnetic field, a lubricant may be added to the raw material powder.
In addition, before forming in a magnetic field as described above, a lubricant may be added to improve the grindability in the step of obtaining the raw material powder by grinding the raw material alloy with an airflow crusher (jet mill) or the like. Yes (see, for example, Patent Document 1).

JP-A-8-111308 (Claims)

In order to improve the grindability of the raw material alloy in the grinding step and to improve the orientation of the raw material powder in the forming step in a magnetic field, it is preferable to increase the amount of lubricant added. However, an increase in the amount of lubricant to be added leads to a decrease in the magnetic properties of the obtained rare earth sintered magnet.
Moreover, the lubricant aggregated particles remain only by adding, and voids resulting from the aggregated particles are formed in the sintered body after sintering. Furthermore, the strength of the molded body is reduced by the added lubricant. It is also known that peeling or cracking occurs in the molded body, making it difficult to obtain a sintered body with desired dimensional accuracy (see, for example, Patent Document 2).

Japanese Patent Laid-Open No. 7-240329 (problem to be solved by the invention)

  The present invention has been made on the basis of such a technical problem, and rare earth sintering capable of obtaining a high-strength molded article and a rare earth sintered magnet having high magnetic properties by suppressing the amount of lubricant added as much as possible. It aims at providing the manufacturing method of a magnet, and the grinding | pulverization method of the raw material alloy powder for sintered magnets.

In the course of earnest studies to solve the above problems, the present inventors paid attention to the dispersibility of the lubricant with respect to the raw material alloy in the pulverization step. The inventor initially thought that the lubricant was sufficiently pulverized by the airflow pulverizer. However, it has been found that the lubricant is not pulverized like the raw material alloy of the rare earth sintered magnet. Therefore, in order to improve the dispersibility of the lubricant with respect to the raw material alloy, it has been considered that it is effective to reduce the particle size of the lubricant to be added.
The method for producing a rare earth sintered magnet of the present invention thus made comprises a step of pulverizing a lubricant to obtain lubricant particles having a particle size not more than 1.5 times the particle size of the raw material alloy powder, A step of adding agent particles to the raw material alloy powder and pulverizing to obtain a pulverized powder, a step of applying a magnetic field to the pulverized powder and press-molding, and a step of sintering the compact It is characterized by providing.
As described above, when the lubricant particles having a predetermined particle size with respect to the particle size of the raw material alloy powder are added to the raw material alloy powder and pulverized, the lubricant is more uniformly dispersed. Thereby, the grindability of the raw material alloy in the grinding step and the orientation of the ground powder in the forming step in the magnetic field can be improved. Further, since the dispersibility of the lubricant is improved, an equivalent lubricating effect can be expected with a smaller amount of lubricant than in the prior art. In the step of pulverizing the lubricant, the lubricant is preferably pulverized so that the particle size of the lubricant particles is 1.5 times or less than the particle size of the raw material alloy powder. The lubricant particles having such a particle size can be obtained, for example, by pulverizing the lubricant after freezing.

In the present invention, the material of the lubricant is not particularly limited, but the compound A represented by the general formula R ₁ —CONH ₂ or R ₁ —CONH—R ₃ —HNCO—R ₂ , R ₄ —OCO—R ₅ , Compound B represented by any one of the group consisting of R ₄ —OH and (R ₄ —COO) _n M (R _1-4 is C _n H _{2n + 1} or C _n H _2n−1, R ₅ is H, C _n H _{2n + 1} or C _n H _{2n−1, where} M is a metal and n is an integer. In addition, compound A represented by the general formula R ₁ —CONH ₂ or R ₁ —CONH—R ₃ —HNCO—R ₂ , R ₄ —OCO—R ₅ , R ₄ —OH, (R ₄ —COO) _n M compound B _{(R 1 to 4} represented by any one of the group consisting of the or _{C n H 2n + 1 C n} H 2n-1 .R 5 is _{H, C n H 2n + 1} or _C n _{H 2n-1} .M is It is also preferable to use a compound D in which a metal (n is an integer) is bonded via a hydrocarbon.

  In the present invention, the raw material alloy powder and the lubricant particles having a particle size ratio (lubricant particle size / raw material alloy powder particle size) of 1.5 or less are put into a pulverizer to pulverize the raw material alloy powder. There is also provided a method for pulverizing a raw material alloy powder for a sintered magnet, characterized in that pulverized powder is obtained. Lubricant particles having a particle size not larger than 1.5 times the particle size of the raw material alloy powder may be formed by any method. For example, lubricant particles having a desired particle diameter can be obtained by a spray drying method or the like. Alternatively, the lubricant may be frozen and solidified, and the lubricant may be pulverized in this state to obtain lubricant particles having a desired particle size. The raw alloy powder may be pulverized by any method. For example, an airflow pulverizer can be used as the pulverizer. In this case, the lubricant particles together with the raw material alloy powder are put into an airflow pulverizer to pulverize the raw material alloy powder.

  According to the present invention, by adding a lubricant that is pulverized and has a predetermined relationship with the particle size of the raw material alloy powder, the pulverization property of the raw material alloy powder in the pulverization step and the pulverized powder in the forming step in a magnetic field are added. As a result, the strength of the compact and the magnetic properties of the finally obtained rare earth sintered magnet can be improved. In addition, it is possible to obtain the same molded body strength or magnetic characteristics as before with a smaller amount of lubricant.

The present invention can be applied to, for example, a rare earth sintered magnet, particularly an RTB based sintered magnet.
This RTB-based sintered magnet contains 25 to 37 wt% of a rare earth element (R). Here, R in the present invention has a concept including Y, and therefore 1 of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. It is selected from species or two or more species. If the amount of R is less than 25 wt%, the R ₂ T ₁₄ B phase, which is the main phase of the RTB-based sintered magnet, is not sufficiently generated, and α-Fe having soft magnetism is precipitated and retained. Magnetic force is significantly reduced. On the other hand, when R exceeds 37 wt%, the volume ratio of the R ₂ T ₁₄ B phase, which is the main phase, decreases, and the residual magnetic flux density decreases. Further, R reacts with oxygen, the amount of oxygen contained increases, and accordingly, the R-rich phase effective for the generation of coercive force decreases, leading to a decrease in coercive force. Therefore, the amount of R is set to 25 to 37 wt%. A preferable amount of R is 28 to 35 wt%, and a more preferable amount of R is 29 to 33 wt%.

The RTB-based sintered magnet contains 0.5 to 4.5 wt% of boron (B). When B is less than 0.5 wt%, a high coercive force cannot be obtained. On the other hand, when B exceeds 4.5 wt%, the residual magnetic flux density tends to decrease. Therefore, the upper limit of B is set to 4.5 wt%. A preferable amount of B is 0.5 to 1.5 wt%, and a more preferable amount of B is 0.8 to 1.2 wt%.
This RTB-based sintered magnet contains Co of 2.0 wt% or less (excluding 0), desirably 0.1 to 1.0 wt%, and more desirably 0.3 to 0.7 wt%. can do. Co forms the same phase as Fe, but is effective in improving the Curie temperature and improving the corrosion resistance of the grain boundary phase.

In addition, this RTB-based sintered magnet can contain one or two of Al and Cu in the range of 0.02 to 0.5 wt%. By containing one or two of Al and Cu in this range, it is possible to increase the coercive force, the corrosion resistance, and the temperature characteristics of the obtained R-T-B sintered magnet. In the case of adding Al, a preferable amount of Al is 0.03 to 0.3 wt%, and a more preferable amount of Al is 0.05 to 0.25 wt%. In addition, in the case of adding Cu, the preferable amount of Cu is 0.15 wt% or less (not including 0), and the more preferable amount of Cu is 0.03 to 0.12 wt%.
Furthermore, this RTB-based sintered magnet allows the inclusion of other elements. For example, elements such as Zr, Ti, Bi, Sn, Ga, Nb, Ta, Si, V, Ag, and Ge can be appropriately contained. On the other hand, it is preferable to reduce impurity elements such as oxygen, nitrogen, and carbon as much as possible. In particular, the amount of oxygen that impairs magnetic properties is preferably 5000 ppm or less, more preferably 3000 ppm or less. This is because when the amount of oxygen is large, the rare-earth oxide phase, which is a nonmagnetic component, increases and the magnetic properties are deteriorated.

The present invention is not limited to the R-T-B based sintered magnet as described above, but can be applied to other rare earth sintered magnets. For example, the present invention can be applied to an R—Co based sintered magnet.
The R—Co based sintered magnet contains R, one or more elements selected from Fe, Ni, Mn, and Cr, and Co. In this case, it preferably further contains at least one element selected from Cu or Nb, Zr, Ta, Hf, Ti and V, and particularly preferably from Cu and Nb, Zr, Ta, Hf, Ti and V. Containing one or more selected elements. Among these, an intermetallic compound of Sm and Co, preferably an Sm ₂ Co ₁₇ intermetallic compound, is the main phase, and a subphase mainly composed of SmCo ₅ is present at the grain boundary. The specific composition may be appropriately selected according to the production method, required magnetic characteristics, and the like. For example, R: 20 to 30 wt%, particularly about 22 to 28 wt%, Fe, Ni, Mn, and Cr Above: about 1 to 35 wt%, one or more of Nb, Zr, Ta, Hf, Ti and V: 0 to 6 wt%, especially about 0.5 to 4 wt%, Cu: 0 to 10 wt%, especially 1 to 10 wt% To the extent, the composition of Co: remainder is preferred.
The R-T-B sintered magnet and the R-Co sintered magnet have been described above, but the present invention does not prevent application to other rare earth sintered magnets.

Hereinafter, a method for producing a rare earth sintered magnet according to the present invention will be described in the order of steps.
The raw material alloy can be produced by a strip casting method or other known melting methods in a vacuum or an inert gas, preferably an argon atmosphere. In the strip casting method, a molten metal obtained by melting a raw metal in a non-oxidizing atmosphere such as an argon gas atmosphere is jetted onto the surface of a rotating roll. The melt rapidly cooled by the roll is rapidly solidified in the form of a thin plate or flakes (scales). This rapidly solidified alloy has a homogeneous structure with a crystal grain size of 1 to 50 μm. The raw material alloy can be obtained not only by the strip casting method but also by a melting method such as high frequency induction melting. In order to prevent segregation after dissolution, for example, it can be solidified by pouring into a water-cooled copper plate. An alloy obtained by the reduction diffusion method can also be used as a raw material alloy.
When obtaining an RTB-based sintered magnet, a so-called alloy using a R ₂ T ₁₄ B crystal grain (low R alloy) and an alloy containing more R than a low R alloy (high R alloy) is used. A mixing method can also be applied to the present invention.

First, the raw material alloy is subjected to a grinding process. In the case of the mixing method, the low R alloy and the high R alloy are pulverized separately or together. The pulverization process includes a coarse pulverization process and a fine pulverization process.
In the coarse pulverization step, the raw material alloy is coarsely pulverized to a particle size of about several hundred μm to obtain a coarsely pulverized powder. This coarsely pulverized powder corresponds to the raw material alloy powder in the present invention. The coarse pulverization is preferably performed in an inert gas atmosphere using a stamp mill, a jaw crusher, a brown mill or the like. Prior to coarse pulverization, it is effective to perform pulverization by allowing hydrogen to be stored in the raw material alloy and then releasing it. The hydrogen releasing treatment is performed for the purpose of reducing hydrogen as an impurity as a rare earth sintered magnet. The temperature of heating and holding for releasing hydrogen is 200 ° C. or higher, desirably 350 ° C. or higher. The holding time varies depending on the relationship with the holding temperature, the thickness of the raw material alloy, etc., but is at least 30 minutes or longer, preferably 1 hour or longer. The hydrogen release treatment is performed in a vacuum or with an argon gas flow. The hydrogen storage process and the hydrogen release process are not essential processes. This hydrogen pulverization can be regarded as coarse pulverization, and mechanical coarse pulverization can be omitted.

After the coarse pulverization process, the process proceeds to the fine pulverization process.
At this time, a lubricant is added for the purpose of improving grindability in the fine grinding step. Examples of the lubricant include fatty acids or fatty acid derivatives such as stearic acid-based and oleic acid-based zinc stearate, calcium stearate, stearamide, and oleic acid amide. Various ester-based and alcohol-based derivatives can also be used. These lubricants can also function to improve lubrication and orientation during molding.

As the lubricant, the compound A represented by the general formula R ₁ —CONH ₂ or R ₁ —CONH—R ₃ —HNCO—R ₂ , R ₄ —OCO—R ₅ , R ₄ —OH, (R ₄ —COO) may be used. ) _n M (M is a metal, n represents the compound B represented by one any of the group consisting of integers) _{(R 1 to 4} is or _{C n H 2n + 1 C n} H 2n-1 .R 5 is H, _{C n} It is preferable to use a mixture containing H _{2n + 1} or C _n H _2n-1 .

Compound A is, for example, a compound having an amide group such as fatty acid amide or a compound having an amide bond such as fatty acid bisamide. R ₁ and R ₂ are preferably straight-chain saturated hydrocarbons having 7 to 21 carbon atoms. Such stearic acid amide Specific examples of the compound _{A (C 17 H 35 -CONH 2} ), ethylene bis-stearic acid amide _{(C 17 H 35 -CONH- (CH} 2) 2 -NHCO-C 17 H 35), behenic An acid amide (C ₂₁ H ₄₃ —CONH ₂ ) and caprylic acid amide (C ₇ H ₁₅ —CONH ₂ ) can be mentioned, and among these, stearic acid amide is particularly preferable. In the present invention, compound A may be a single type of compound, or may be a combination of a plurality of compounds.

Compound B is, for example, a fatty acid compound or alcohol, and specific examples include higher fatty acids having 10 or more carbon atoms, higher fatty acid esters, higher fatty acid metal salts, higher alcohols, and the like. Among them, the compound B is preferably a compound in which R ₄ is a hydrocarbon having 17 and 18 carbon atoms. Specific examples include stearic acid (C ₁₇ H ₃₅ —COOH) and glyceryl monostearate (C ₁₇ H ₃₅ —COO—C). ₃ H ₇ O _2), zinc stearate ^{_{((C 17 H 35 -COO)}} - can be exemplified 2 ^{Zn 2+)} and stearyl alcohol _{(C 18 H 37 -O-H} ). Of these, stearic acid and glyceryl monostearate are more preferable, and stearic acid is particularly preferable. As compound B, only one type of compound may be used, or a plurality of compounds may be used in combination.

In addition, compound D in which compound A and compound B are bonded via a hydrocarbon can also be used as a lubricant. For example, there may be mentioned compounds having an amide bond and an ester _{bond, R 6 -CONH-R 7 -OCO} -R 6 (R 6, R 7 is a hydrocarbon) is a compound represented by. Specifically, R ₆ is a compound represented by C _n H _{2n + 1} (n is 12 or more and 17 or less), among which stearoid ethyl stearate (C ₁₇ H ₃₅₎ composed of stearic acid having 17 carbon atoms in R. It is also preferable to use CONH (CH ₂ ) ₂ OCOC ₁₇ H ₃₅ ) as a lubricant.

  As the lubricant, a lubricant (lubricant particles) in which the lubricant is pulverized in advance to reduce the particle size can be used. Specifically, the particle size of the lubricant particles is 1.5 times the particle size of the raw material alloy powder (particle size ratio (the particle size of the lubricant / the particle size of the raw material alloy powder) is 1.5) or less. Grind the lubricant. Preferably, the particle size of the lubricant particles is 1.0 times (particle size ratio is 1.0) or less, more preferably 0.7 times (particle size ratio is 0.7) or less that of the raw material alloy powder. . For example, when the particle size of the coarsely pulverized powder is about 100 to 1000 μm, the particle size of the lubricant particles is 150 μm or less to 1500 μm or less, preferably 100 μm or less to 1000 μm or less, and more preferably 70 μm or less to 700 μm or less. The lubricant particles may be formed by any method. For example, lubricant particles having a desired particle diameter can be obtained by a spray drying method or the like. Alternatively, the lubricant may be frozen and solidified using liquid nitrogen, and the lubricant particles having a desired particle diameter may be obtained by pulverizing the lubricant with a pulverization mill or the like in that state. Further, the lubricant particles may be classified with a sieve or the like after the lubricant is pulverized in order to obtain the above particle diameter.

  The addition amount of the lubricant having a predetermined particle size is preferably as much as possible from the viewpoint of improving the grindability, but it is as small as possible from the viewpoint of magnetic properties and strength of the molded body. Is preferred. Therefore, the amount of lubricant added is preferably 0.01 to 1.0 wt%. In the present invention, in order to improve the dispersibility, the additive amount of the lubricant can be reduced to 0.5 wt% or less, further 0.3 wt% or less. Mixing of the lubricant and the coarsely pulverized powder may be performed for about 5 to 30 minutes using, for example, a Nauter mixer.

  Now, an airflow pulverizer is mainly used for fine pulverization of the coarsely pulverized powder to which the lubricant is added. By pulverizing the coarsely pulverized powder, the average particle size is 2.5 to 6 μm, desirably 3 to 5 μm. A finely pulverized powder (ground powder) is obtained. The airflow type pulverizer generates a high-speed gas flow by opening a high-pressure inert gas through a narrow nozzle, accelerates the coarsely pulverized powder by this high-speed gas flow, and collides between coarsely pulverized powders, targets or container walls. This is a method of pulverizing by causing a collision.

  In the case of the mixing method, the timing of mixing the two kinds of alloys is not limited. However, when the low R alloy and the high R alloy are separately pulverized in the pulverization step, the pulverized low R alloy powder is used. And high R alloy powder in a nitrogen atmosphere. The mixing ratio of the low R alloy powder and the high R alloy powder may be about 80:20 to 97: 3 by weight. The mixing ratio when the low R alloy and the high R alloy are pulverized together is the same.

The finely pulverized powder obtained as described above is filled in a mold cavity and subjected to molding in a magnetic field.
The molding pressure in the magnetic field molding may be in the range of 0.3 to 3 ton / cm ² (30 to 300 MPa). The molding pressure may be constant from the start to the end of molding, may increase or decrease gradually, or may vary irregularly. The lower the molding pressure is, the better the orientation is. However, if the molding pressure is too low, the strength of the molded body is insufficient and handling problems occur. Therefore, the molding pressure is selected from the above range in consideration of this point. The final relative density of the molded body obtained by molding in a magnetic field is usually 50 to 60%.
The applied magnetic field may be about 12 to 20 kOe (960 to 1600 kA / m). Further, the applied magnetic field is not limited to a static magnetic field, and may be a pulsed magnetic field. A static magnetic field and a pulsed magnetic field can also be used in combination.

  Next, the compact obtained by molding in a magnetic field is sintered in a vacuum or an inert gas atmosphere. Although it is necessary to adjust sintering temperature by various conditions, such as a composition, a grinding | pulverization method, a difference of an average particle diameter, and a particle size distribution, what is necessary is just to sinter at 1000-1200 degreeC for about 1 to 10 hours in a vacuum.

  Now, after sintering, the obtained sintered body can be subjected to an aging treatment. This process is an important process for controlling the coercive force. When the aging treatment is performed in two stages, holding for a predetermined time at 750 to 1000 ° C. and 500 to 700 ° C. is effective. When the heat treatment at 750 to 1000 ° C. is performed after sintering, the coercive force increases, which is particularly effective in the mixing method. In addition, since the coercive force is greatly increased by heat treatment at 500 to 700 ° C., the aging treatment at 500 to 700 ° C. is preferably performed when the aging treatment is performed in one stage.

The composition of the raw material alloy was 24.5 wt% Pr-6.0 wt% Dy-1.8 wt% Co-0.5 wt% Al-0.2 wt% Cu-0.07 wt% B-1.0 wt% Fe. The raw material alloy thin plate was melted and cast by a strip casting method. The obtained raw material alloy thin plate was hydrogen pulverized and then mechanically coarsely pulverized by a brown mill to obtain coarsely pulverized powder. The coarsely pulverized powder had a flat plate shape, and had a thickness of about 100 to 300 μm and a size (length) of about 100 to 1000 μm. This was classified by sieving.
Further, oleic amide as a lubricant was frozen in liquid nitrogen and pulverized using a pulverizing mill. The obtained lubricant (lubricant particles) was classified by sieving.

The classified coarsely pulverized powder and the classified lubricant were finely pulverized in the combinations shown in Table 1, respectively. The amount of lubricant added is 0.1 wt%. An airflow type pulverizer was used for fine pulverization, and fine pulverization was performed in a high-pressure nitrogen gas atmosphere at a pulverization gas pressure of 7 kg / cm ² and an input speed of 40 g / min. The particle size distribution of the finely pulverized powder obtained is measured and the particle size (D50 = particle size at which the cumulative volume ratio becomes 50%) is determined and shown in Table 1.

  As can be seen from Table 1, the finer the particle size of the lubricant, the better the grinding efficiency and the smaller the particle size (D50) of the finely pulverized powder. Thus, it is considered that the lubricant having a small particle diameter has improved dispersibility, and as a result, the pulverization efficiency has been improved.

Next, in the same manner as described above, the lubricant is classified into a particle size of 20 μm or more and less than 100 μm (may be expressed as 20 to 100 μm, hereinafter the same), 200 μm or more and less than 500 μm, 500 μm or more and less than 800 μm, or 800 μm or more and less than 1000 μm. Then, coarsely pulverized powders classified into less than 100 μm, 200 μm or more and less than 500 μm, 500 μm or more and less than 800 μm, or 800 μm or more and less than 1100 μm were prepared and combined as shown in Table 2 to obtain finely pulverized powder. The amount of lubricant added in each classification was 0.02 wt%, 0.06 wt%, or 0.1 wt%. In addition, since the pulverization efficiency of the finely pulverized powder varies depending on the particle diameter and the amount of addition of the lubricant, when the pulverization process is performed in the same manner as the above method, the pulverization time is adjusted in each case, and the finally obtained finely pulverized powder The particle size (D50) was adjusted to 4.40 μm <D50 <4.60 μm. In addition, the direction which grind | pulverized the coarsely pulverized powder with a big particle size tended to take time. Table 2 shows the particle diameter ratio (the particle diameter of the lubricant / the particle diameter of the coarsely pulverized powder) calculated from the particle diameter of the obtained lubricant and the particle diameter of the coarsely pulverized powder. In the calculation of the particle size ratio, each particle size is defined as the particle size with the center value of the particle size range by classification. For example, the particle size was determined such that 60 μm for 20-100 μm and 350 μm for 200-500 μm.
Furthermore, as a comparative example, a finely pulverized powder was prepared in the same manner as in the example except that an unpulverized lubricant and an unclassified coarsely pulverized powder were used.

Each of the finely pulverized powders thus obtained was molded in a magnetic field. Specifically, molding was performed at a pressure of 140 MPa in a magnetic field of 15 kOe to obtain a molded body of 20 mm × 18 mm × 6 mm.
As the strength of the obtained molded body, the bending strength was measured by the following method. The bending strength measurement was performed according to Japanese Industrial Standard JIS R 1601. Specifically, as shown in FIG. 5, the molded body 11 is placed on the two round bar-shaped supports 12 and 13, and the round bar-shaped support 14 is arranged at the center position on the molded body 11. The load was applied. The direction in which the bending pressure was applied was the pressing direction. The radius of the round bar-shaped supports 12, 13, and 14 was 3 mm, the distance between fulcrums was 10 mm, and the load point moving speed was 0.5 mm / min. The longitudinal direction of the molded body 11 and the support 14 were arranged so as to be parallel to each other. The measurement was carried out with 10 samples. Although the strength of the compact varies depending on the particle diameter, in this embodiment, the particle diameter of the finely pulverized powder is within the predetermined range (4.40 μm <D50 <4.60 μm) as described above. It is easy to compare body strength.

  Furthermore, the obtained molded body was fired at 1030 ° C. for 4 hours to obtain a sintered body. The obtained sintered body was subjected to an aging treatment (conditions: 900 ° C. for 1 hour, 530 ° C. for 1 hour) to obtain a rare earth sintered magnet, and then the residual magnetic flux density (Br) of the rare earth sintered magnet was determined. Measured with a BH tracer.

In FIG. 1, Example A (particle size ratio 1.20) in which the particle size of the coarsely pulverized powder shown in Table 2 is less than 100 μm and Comparative Examples B to E (particle size ratios 7.00, 13.00, 18. (00, no pulverization) The relationship between the strength of the compact and the magnetic properties is shown in a graph.
FIG. 2 shows Examples F and G (particle size ratios 0.17 and 1.00) in which the particle size of the coarsely pulverized powder shown in Table 2 is 200 to 500 μm and Comparative Examples H to J (particle size ratio 1.86). , 2.57, no pulverization) is a graph showing the relationship between the strength of the compact and the magnetic properties.
3, Examples K to N (particle size ratios 0.09, 0.54, 1.00, 1.38) in which the particle size of the coarsely pulverized powder shown in Table 2 is 500 to 800 μm and Comparative Example O ( The relationship between the strength of the green compact and the magnetic properties is shown in a graph.
FIG. 4 shows Examples P to S (particle size ratios 0.06, 0.37, 0.68, 0.95) in which the particle size of the coarsely pulverized powder shown in Table 2 is 800 to 1000 μm, and Comparative Example T ( The relationship between the strength of the green compact and the magnetic properties is shown in a graph.
In FIG. 1 to FIG. 4, the results when the amount of lubricant added is 0.02 wt%, 0.06 wt%, and 0.1 wt% in order from the lower residual magnetic flux density (Br) to the higher one. Show. In the captions in the figure, the numbers indicate the particle size ratio (lubricant particle size / coarse pulverized powder particle size). “Original” shown in the figure indicates the result of using an unground lubricant and unclassified coarsely ground powder.

As can be seen from FIGS. 1 to 4, when the addition amount is changed without changing the particle size of the coarsely pulverized powder, the larger the addition amount of the lubricant, the better the dispersion of the lubricant. As a result of easy orientation, the residual magnetic flux density (Br) was improved. Further, in this case, the bonding strength between the particles became weak, so that the molding strength tended to decrease. As can be seen by comparing the examples of FIGS. 1 to 4 for each figure, the finer the particle size of the lubricant, the better the dispersion of the lubricant, the easier the magnetic orientation, and the residual magnetic flux density (Br). Improved.
Further, as can be seen by comparing FIGS. 1 to 4, the larger the particle size of the coarsely pulverized powder, the larger the residual magnetic flux density (Br) tended to be observed. In particular, it was remarkable in Examples having a particle size ratio of 1.5 or less. This seems to be because the pulverization time is long in order to make the particle size of the finely pulverized powder uniform, and the lubricant is well dispersed accordingly.

  By the way, the rare earth sintered magnet is required to have a high compact strength in the manufacturing process and a high residual magnetic flux density (Br) as the rare earth sintered magnet. In each of the graphs of FIGS. 1 to 4, this requirement is met as the plot is in the upper right. As shown in FIGS. 1 to 4, the lower the particle size ratio using a finer particle lubricant, the more this requirement is met. In addition, as can be seen from FIGS. 1 to 4, when a lubricant having a particle size larger than the particle size of the coarsely pulverized powder and a large particle size ratio is used, it is pulverized as indicated by “original” in the drawing. The results were not significantly different from the results obtained when using a non-classified lubricant and unclassified coarsely pulverized powder.

  As described above, as a fine particle size lubricant, by adjusting the particle size of the lubricant so that the particle size ratio is particularly 1.5 or less, excellent strength and magnetic properties of the molded product can be obtained, Further, when the particle size ratio is 1.0 or less, particularly 0.7 or less, the magnetic properties and the strength of the molded product are remarkably improved. On the other hand, when the particle size of the lubricant is large and the particle size ratio is large as in the comparative example, it is difficult to disperse and the effect of lubricating the coarsely pulverized powders cannot be sufficiently obtained. From this, by adding a lubricant with a particle size ratio of 1.5 or less in the fine pulverization process, the pulverization of the raw material alloy in the pulverization process and the orientation of the raw material powder in the forming process in a magnetic field are ensured. In addition, the strength of the compact and the magnetic properties of the finally obtained rare earth sintered magnet can be improved. In other words, it has been found that it is possible to obtain the same molded body strength or magnetic properties as conventional with a smaller amount of lubricant than before.

  A coarsely pulverized powder (particle size: less than 200 to 500 μm) was prepared in the same manner as in Example 1. As a lubricant, 0.05% by weight of each of Compound A and Compound B shown in Table 3, or 0.1% by weight of each of Compound A and Compound B was added to the coarsely pulverized powder. The lubricants (Compound A and Compound B) are both adjusted to have a particle size of less than 300 μm. Therefore, the particle size ratio of Example 2 is 0.43. Subsequently, fine pulverization was performed using an airflow pulverizer in a high-pressure nitrogen gas atmosphere so that the average particle diameter D50 was 4.1 μm.

  The obtained finely pulverized powder was molded in a magnetic field to obtain a molded body having a predetermined shape. In the molding in a magnetic field, the finely pulverized powder was molded at a molding pressure of 150 MPa in a magnetic field of 15 kOe. The magnetic field direction is a direction perpendicular to the pressing direction. As the dimensions of the molded body, two types of 20 mm × 18 mm × 6.5 mm (molded body a) and 20 mm × 18 mm × 13 mm (molded body b) were obtained. And the molded object strength was measured like Example 1 using the molded object a. The results are shown in Table 3.

  After the compact b was sintered at 1030 ° C. for 4 hours, an aging treatment was performed at 900 ° C. for 1 hour and 530 ° C. for 1 hour. The surface of the obtained sintered body was ground to obtain a rectangular parallelepiped sample. This sample was evaluated for magnetic properties using a BH tracer. The results are shown in Table 3.

As shown in Table 3, when only compound A was added, the compact strength was 1.05 MPa or more, but Br was less than 13.2 kG, and when only compound B was added, Br was 13.2 kG. However, the strength of the compact was below 0.9 MPa. That is, when only compound A is added, high magnetic strength can be obtained, but the magnetic properties are low, and when only compound B is added, high magnetic properties can be obtained, but the strength of the compact is low. It was.
On the other hand, when both Compound A and Compound B were added, Br exceeded 13.2 kG, and the compact strength exceeded 1.05 MPa. That is, it was confirmed that the compound A and the compound B can be combined to have high molded body strength and high magnetic properties. Moreover, it can be seen that the strength and magnetic properties of the obtained molded product are equal to or higher than the strength of the molded product when Compound A is added alone and the magnetic property when Compound B is added alone.

  As a lubricant, a sample was prepared in the same manner as in Example 2 except that the mixing ratio of stearic acid amide of compound A and the mixing ratio of stearic acid of compound B were mixed in the ratio shown in Table 4 and added so that the total amount was 0.1 wt%. Were obtained, and a compact and a rare earth sintered magnet were obtained, and the strength and magnetic properties of the compact were evaluated. The results are shown in Table 4.

  As shown in Table 4, when the compounding ratio of Compound B is 75% or more, the strength of the compact is less than 1.05 MPa. Therefore, it can be said that it is preferable that the mixing ratio of the compound A and the compound B is 9: 1 to 1: 2 on a weight basis. Further, since a high Br of 13.25 kG or more can be obtained, a more preferable range of the mixing ratio of Compound A and Compound B is 9: 1 to 1: 1, and particularly preferable is approximately 1: 1.

  As a lubricant, a sample was prepared in the same manner as in Example 2 except that the mixing ratio of stearic acid amide of compound A and stearic acid of compound B was 1: 1 and the addition amount was added as shown in Table 5. A compact and a rare earth sintered magnet were obtained, and strength and magnetic properties were evaluated. The results are shown in Table 5.

  As shown in Table 5, when compound A and compound B are mixed at approximately 1: 1, the amount of lubricant added is in the range of 0.075 to 0.1 wt%, and Br is 13.2 kG or more. And the strength of the compact is 1.05 MPa or more. Thereby, when compound A and compound B are mixed by about 1: 1, it can be said that it is preferable that the addition amount of a lubricant shall be 0.075-0.1 wt% in total.

  A sample was prepared in the same manner as in Example 2 except that 0.1 wt% of stearoid ethyl stearate was added as a lubricant to be added to the raw material alloy coarse powder, and a molded body and a rare earth sintered magnet were obtained and evaluated. The results obtained are shown in Table 6.

  As shown in Table 6, even when stearoid ethyl stearate was added, Br was 13.2 kG or more as in the case of compound addition of compounds A and B as shown in Examples 2 to 4, In addition, it was confirmed that the strength of the molded body was 1.05 MPa or more.

It is a graph which shows the relationship between a molded object strength and a magnetic characteristic when changing the particle size of lubricant particle | grains with respect to the coarsely pulverized powder whose particle size is less than 100 micrometers. It is a graph which shows the relationship between a molded object strength and a magnetic characteristic when changing the particle size of lubricant particle | grains with respect to the coarsely pulverized powder with a particle size of 200-500 micrometers. It is a graph which shows the relationship between a molded object strength and a magnetic characteristic when changing the particle size of lubricant particle | grains with respect to the coarsely pulverized powder with a particle size of 500-800 micrometers. It is a graph which shows the relationship between a molded object strength and a magnetic characteristic when changing the particle size of lubricant particle | grains with respect to the coarsely pulverized powder with a particle size of 800-1000 micrometers. It is a figure which shows the measuring method of the bending strength of a molded object.

Claims (7)

Pulverizing the lubricant to obtain lubricant particles having a particle size not more than 1.5 times the particle size of the raw material alloy powder;
Adding and pulverizing the lubricant particles to the raw material alloy powder to obtain a pulverized powder;
Applying a magnetic field to the pulverized powder, and obtaining a molded body by pressure molding; and
Sintering the molded body;
A method for producing a rare earth sintered magnet.   2. The rare earth sintered magnet according to claim 1, wherein in the step of pulverizing the lubricant, the lubricant is pulverized so that a diameter of the lubricant particles is equal to or less than a particle diameter of the raw material alloy powder. Manufacturing method.   The method for producing a rare earth sintered magnet according to claim 1, wherein in the step of pulverizing the lubricant, the lubricant particles are obtained by pulverizing the lubricant after freezing. The lubricant is
Compound A represented by the general formula _R 1 -CONH ₂ or _{R 1 -CONH-R 3 -HNCO-} R 2,
Compound B represented by any one of the group consisting of R ₄ —OCO—R ₅ , R ₄ —OH, and (R ₄ —COO) _n M (R _1-4 is C _n H _{2n + 1} or C _n H _{2n— 1.} R ₅ is H, C _n H _{2n + 1} or C _n H _2n−1, M is a metal, and n is an integer.) Rare earth sintering according to claim 1, Magnet manufacturing method. The lubricant is
Compound A represented by the general formula _R 1 -CONH ₂ or _{R 1 -CONH-R 3 -HNCO-} R 2,
Compound B represented by any one of the group consisting of R ₄ —OCO—R ₅ , R ₄ —OH, and (R ₄ —COO) _n M (R _1-4 is C _n H _{2n + 1} or C _n H _{2n— 1.} R ₅ is H, C _n H _{2n + 1} or C _n H _2n-1, M is a metal, and n is an integer), and is a compound D bonded with a hydrocarbon. 4. A method for producing a rare earth sintered magnet according to any one of 3 above.   Raw material alloy powder and lubricant particles having a particle size ratio (lubricant particle size / raw material alloy powder particle size) of 1.5 or less are charged into a pulverizer, and the raw material alloy powder is pulverized to be pulverized powder. A method for pulverizing a raw material alloy powder for a sintered magnet.   The method for pulverizing a raw material alloy powder for a sintered magnet according to claim 6, wherein an airflow pulverizer is used as the pulverizer.

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